1. Field of the Invention
The present invention relates to open-cell resilient foam materials, and particularly to resilient foam materials for use as a carpet cushion underlay.
2. Prior Art
One of the outstanding advances in the plastics industry has been the development of polyurethane foams which are cellular plastic materials generally formed by the reaction of long chain polyol compounds and organic polyisocyanates. Cellular plastics are available in various degrees of rigidity, ranging from soft, flexible foams useful in cushioning, clothing interliners, rug underlays, sponges and bath mats; semi-rigid foams, useful particularly as crash pads; and rigid foams for structural and insulation purposes. The final properties of the urethane foams depend principally on the choice of polyethers, polyesters or other long chain polyhydroxyl compounds which are converted by the polyisocyanate into a high molecular weight polymer which is then foamed by a suitable foaming system, usually a reaction of water with the free isocyanate content of the polymer, resulting in the formation of carbon dioxide which expands the resin into the desired cellular plastic. The control of branching in the reactants permits an extremely wide range of properties in the final foamed plastic. The density of the foam is controlled to a great extent by the amount of water employed. The configuration of the cell depends principally on the equivalent weight of the long chain polyhydroxyl materials favoring the production of a closed cell structure and the higher equivalent weight polyhydroxyl materials leading to the open-cell structure. The degree of branching of the polyhydroxyl reactant also influences the cell character.
The flexible and semi-rigid foams are processed for the aforementioned applications in a manner such that the foam has a low density, usually from about 1.25 to 4 pounds per cubic foot, and preferably as low a density as is consistent with the provisions of a product of adequate strength, etc. Moreover, such flexible and semi-rigid foams should have an open-celled structure for most applications, which is to say that essentially all (i.e., at least about 90 per cent), of the cells are intercommunicating since such a foam configuration is essential to the realization of acceptable foams for cushioning, clothing interliners, crash pads or the like. Rigid foams, in contradistinction, may have varying density values ranging up to 30 pounds per cubic foot or higher, and usually have a closed cell structure.
For certain applications, including padding utilized under carpet, however, it is often desired to utilize materials other than polyurethanes. Unfortunately, however, other polymer systems do not lend themselves readily to being formed into opencell, resilient structures. Generally, such structures are formed from latexes containing the desired polymer. The two most widely used procedures are the so-called Dunlap and Taladay foaming methods.
The Dunlap process utilizes a mechanical "foaming machine", e.g., the "Oakes" foamer or "Firestone" foamer whereby air is whipped into an aqueous latex compound (either SBR and/or natural latex). One frothed, a "gelling" agent (sodium silicon fluoride, potassium silicon fluoride and/or ammonium acetate) is introduced to cause the latex system to coagulate and assume a semi-solid (putty-like) consistency which can then be subjected to heat and allowed to cure in order to hold a desired shape. The Dunlap process will not produce a thick foam structure on a continuous basis. It is generally used to produce molded pieces of various thicknesses.
The Taladay method is much like the "Dunlap Process" except that, instead of using a chemical gelation, it freezes the foam by introducing carbon dioxide gas into the system to cause coagulation of the latex. Once coagulated, the normal curing takes place.
It is almost impossible, however, to produce large or continuous foamed materials by these methods higher than about 3/8 inch due to the fact that at the greater heights, the foam cells collapse causing uneven gauge and inferior physical properties.
The qualities of available polymers, however, such as the compression resistance and flexibility of the synthetic and natural rubbers, the fire-retardant properties of polyvinyl chloride, etc., make these systems very desirable for specific applications, e.g., padding materials, especially carpet padding or cushion underlay.
Several prior patents disclose polyurethane foam materials being impregnated with various other compositions in order to obtain changes in particular characteristics of the polyurethane foam, however, none of these patents, discussed briefly below, provides an impregnated polyurethane foam structure having improved properties which are particularly useful as an improved padding or cushion underlay material for use under carpet.
U.S. Pat. No. 4,008,350, issued to Crawford et al, discloses an open-celled polyurethane foam impregnated with acrylic latices. The use described for this product is for a lining or padding material for use between the foot or leg and a ski boot. As indicated in the specification of that patent, the resinous acrylic latices retard the response of the foam to compressive stresses, and slow the tendency of the foam to recover to its original dimensions. As such, the product is not well suited for use as a carpet cushion underlay.
U.S. Pat. No. 4,169,184, issued to Pufahl, discloses a pressure sensitive adhesive structure. The polyurethane foam disclosed therein is to some extent (approximately 40%) opencelled, but it is a high density polyurethane, ranging from between 20-60 lbs./ft..sup.3. The end product is made from this high density base foam having a thickness in the range of 15-35 mils, and is impregnated with a polychloroprene (neoprene) latex. Such a product would not yield a useful material for a carpet cushion underlay material.
U.S. Pat. No. 4,279,953, issued to Barden et al, discloses a heat resistant product for use between an automobile floorboard and the floor carpeting in the automobile. This product is not intended to be used as a cushion or padding, nor would it perform particularly well in such service. This patent teaches the use of carboxylated styrene-butadiene rubber (SBR) as an impregnating material, and only the outer surface portions of a polyurethane foam are impregnated. Carboxylated SBR imparts little or no resiliency to the final product, and the less than complete impregnation of the polyurethane foam provides no substantial improvement in resiliency of the foam.
U.S. Pat. No. 4,288,559, issued to Illger et al discloses the use of a foam material, preferably a polyurethane foam, impregnated with a dispersion of aluminum hydroxide, polyurethane latex and mixing stabilizers. The end product in this patent is touted as providing a foam material having increased flame resistance without impairment of the mechanical properties of the foam. As indicated previously, polyurethane foam has shortcomings in several respects for use as a carpet cushion underlay.
U.S. Pat. Nos. 4,547,526 and 4,455,396, issued to Al-Tabaqchali et al disclose a polyurethane foam impregnated with an aqueous dispersion of an acrylate and a flame protection agent which includes a aluminum trihydrate. Like the Illeger et al patent discussed above, the products disclosed are directed to providing increased resistance to flame without impairment of the original mechanical properties of the foam. The use of an acrylate in the impregnant is indicated as providing better resistance to aging than a polychloroprene latex would provide.
U.S. Pat. No. 4,239,571, issued to Cobb, is directed to a polyurethane foam which is impregnated with a liquid thermosetting resin which is cured while the foam is in compression. The resulting structure is not open-celled and is not sufficiently resilient for use as a carpet cushion underlay.
U.S. Pat. No. 4,224,374, issued to Priest, discloses a polyurethane foam substrate impregnated with a carboxylated neoprene latex mixture having alumina trihydrate included for increased fire resistance. Like the products disclosed in the Illger et al and Al-Tabaqchali et al patents, the object of impregnating the foam is to impart fire or flame resistance to the foam without affecting or impairing the mechanical properties of the substrate.
U.S. Pat. No. 4,260,688, issued to Simon, discloses yet another approach to flame-proofing a polyurethane foam without disturbing the physical properties of the foamed plastic. This patent discloses an impregnant including a carboxylated vinylidene-butadiene copolymer and aqueous ammoniacal combinations of benzenephosphonic acid and melamine salts.
U.S. Pat. No. 4,042,746, issued to Hofer, discloses a multilayered composite structure having a rigid foam core member. One or more open-celled, initially resilient polyurethane foam layers are impregnated with a thermosetting or polymerizable liquid resin which is cured under compression with the rigid foam core at the center and a reinforcing fiberglass layer laminated at an outer surface. The resulting structure is not resilient, and in that respect it could not be used as a padding or cushion material for carpet.
The systems and methods described in the above-identified patents are found lacking in disclosing an improved carpet cushion underlay having an impregnated foam structure. Further, none of the prior art systems disclose the impregnation of a foamed material with a solution containing greater than 80% solids, and up to 88% solids. The preferred ranges in these patents go up to only about 60-65% solids, and only the Illger et al patent discusses the possibility of using a solution having up to 80% solids.
It is therefore a principal object of the present invention to provide an improved carpet padding or carpet cushion underlay having improved mechanical properties over unimpregnated low-density polyurethane foams.
It is a further object of the present invention to provide an improved carpet padding structure having an open-celled polyurethane form carrier impregnated with a latex containing a cold or non-carboxylated styrene-butadiene copolymer or a natural rubber or a combination of these two, the structure further having a substrate or scrim bonded thereto by adhesive or by the dried impregnant.
It is a further object of the present invention to provide a novel method for forming a carpet padding structure.